The present invention relates to avionics, and more particularly to altitude displays and terrain awareness warning systems.
A conventional altitude display for a terrain awareness warning system (TAWS) for a given aircraft provides a pilot with a visual display of the terrain having an altitude higher than the aircraft, as well as the terrain within some distance, usually 2000xe2x80x2, below an aircraft.
Referring to prior art FIG. 1, an environment is shown in which a conventional altitude display could be important. In situation I, an aircraft 12 is flying at an altitude X along a direction vector 16. In situation II, an aircraft 12xe2x80x2 is flying at an altitude Xxe2x80x2 along a direction vector 16xe2x80x2. In situation III, an aircraft 12xe2x80x3 is flying at an altitude Xxe2x80x3 along a direction vector 16xe2x80x3. Finally, in situation IV, an aircraft 12xe2x80x2xe2x80x3 is flying at an altitude Xxe2x80x2xe2x80x3 along a direction vector 16xe2x80x2xe2x80x3. The aircrafts 12, 12xe2x80x2, 12xe2x80x3, and 12xe2x80x2xe2x80x3 are flying with direction vectors 16, 16xe2x80x2, 16xe2x80x3, 16xe2x80x2xe2x80x3, respectively, such that an obstruction 14 having height Y is within a forward arc, centered on the respective direction vector, as monitored by the conventional altitude display aboard each respective aircraft.
Starting by considering situation IV, a conventional altitude display would typically give a visual signal as the height Y of the obstruction 14 is greater than the altitude Xxe2x80x2xe2x80x3 of the aircraft 12xe2x80x2xe2x80x3. In other words, Xxe2x80x2xe2x80x3xe2x89xa6Y. An audible alert may be given as well if suitable criteria regarding time-to-impact of the terrain feature are also met. In all cases, the height Y and altitude Xxe2x80x2xe2x80x3 may be measured by radio height, altitude above sea level, or other means, and preferably the same type of measurement, is employed for both distances. The visual signal in this situation would typically be a red area, such as a spot or square, on a cockpit display. The term xe2x80x98REDxe2x80x99 is shown in the figure to denote the range of operation which would result in a red area being displayed. The red area would be indicated to be at a range Z and at a bearing corresponding to the direction of the obstruction 14 relative to the centerline of the aircraft 12xe2x80x2xe2x80x3.
In situation III, a conventional altitude display would also typically give a red visual signal as the height Y of the obstruction 14 is within a predetermined elevation buffer xe2x80x9cDxe2x80x9d and within a predetermined time-to-impact from the altitude Xxe2x80x3 of the aircraft 12xe2x80x3. This elevation buffer D is typically 700xe2x80x2 or 1000xe2x80x2 during enroute navigation, and the alert would be given if Xxe2x80x3xe2x88x92Yxe2x89xa6D. As before, the red area would be indicated to be at a range Z and at a bearing corresponding to the direction of the obstruction 14 relative to the centerline of the aircraft 12xe2x80x3. Also as before, an audible signal may also be given if certain criteria are met.
In situation II, a conventional altitude display would typically just display a visual signal as the altitude Xxe2x80x2 of the aircraft 12xe2x80x2 is greater, than the predetermined elevation buffer D from the height Y of the obstruction 14, by a first distance d1. In other words, Xxe2x80x2xe2x88x92Yxe2x89xa7D+d1. d1 is also typically 1000xe2x80x2. The aircraft 12xe2x80x2 would not be considered to be completely free of the obstruction 14, however, and for this reason the visual signal would be of a cautionary nature. The visual signal would typically be a yellow area, such as a spot or square, on the cockpit display. As such, xe2x80x98YELLOWxe2x80x99 indicates this range. As with the red areas, the yellow area would be indicated to be at a range Z and at a bearing corresponding to the direction of the obstruction 14 relative to the centerline of the aircraft 12xe2x80x2.
Finally, in situation I, a conventional altitude display would typically just display a visual signal as the altitude Xxe2x80x2 of the aircraft 12xe2x80x2 is greater than the height Y of the obstruction 14 by not only the elevation buffer D and the first distance d1, but also by a second distance d2. In other words, Xxe2x80x2xe2x88x92Yxe2x89xa7D+d1+d2. d2 is again typically 1000xe2x80x2. The aircraft 12 would be considered to be mostly free of the obstruction 14, however, and for this reason the visual signal would typically be a green area, such as a spot or square, on the cockpit display. Again, xe2x80x98GREENxe2x80x99 indicates this range. As with the red and yellow areas, the green area would be indicated to be at a range Z and at a bearing corresponding to the direction of the obstruction 14 relative to the centerline of the aircraft 12.
At higher aircraft altitudes, no colored area, or a black area, would be indicated. Here, xe2x80x98NONExe2x80x99 is shown in the figure to denote this range.
Such altitude displays are clearly useful for warning pilots of impending dangerous terrain. However, such systems fail to account for important factors such as the actual flight path of the aircraft. As a result, their accuracy may be less than desired. For example, if an aircraft is climbing, the above described prior art altitude display may report a red area where one is not warranted. In the same way, if an aircraft is high but descending, the above-described prior art altitude display may display a green area where a red area is warranted.
The present invention overcomes the disadvantages of the prior art noted above.
In one aspect, the invention is directed towards a method for providing an indication of aircraft height relative to an obstruction in a terrain awareness warning system. The method includes steps of receiving a first datum indicative of a geographic feature of an obstruction, receiving a second datum indicative of a lateral distance of the geographic feature from an aircraft, receiving a third datum indicative of a height of the aircraft, receiving a fourth datum indicative of a flight path of the aircraft, calculating a projected height of the aircraft at the location of the obstruction using the first through fourth data, generating a result signal based on the projected height and the first datum, and displaying a colored indication on a display screen based on the generated result signal.
Implementations of the method may include one or more of the following. The first datum may be a height of the obstruction. The colored indication may be a colored area on a display screen having a color such as red, yellow, green, or black. The elevation buffer may be zero. The receiving a fourth datum may further include resolving the flight path of the aircraft into components including a lateral flight path and a vertical flight path. The method may further include: calculating a flight path angle of the aircraft from the received fourth datum, calculating an effective altitude of the aircraft by adding to the third datum a value equal to the second datum multiplied by the tangent of the flight path angle, generating a first alert signal if the effective altitude is less than the sum of the first datum and a elevation buffer, sounding an audible alarm with the first alert signal, displaying a first colored indication at a display location corresponding to the second datum as the first alert signal, generating a second alert signal if the effective altitude is greater than the sum of the first datum and a-elevation buffer but less than a sum of the first datum, the elevation buffer, and a first distance, or displaying a second colored indication at a display location corresponding to-the second datum as the second alert signal.
In another aspect, the invention is directed towards a computer program, stored in a machine-readable format, for a terrain awareness warning system. The program causes a computer to: receive a first datum indicative of a geographic feature of an obstruction; receive a second datum indicative of a lateral distance of the geographic feature from an aircraft; receive a third datum indicative of a height of the aircraft; receive a fourth datum indicative of a flight path of the aircraft; calculate a projected height of the aircraft at the location of the obstruction using the first through fourth data; and generate a result signal based on the projected height and the first datum.
In yet another aspect, the invention is directed towards an apparatus for providing an indication of aircraft height relative to an obstruction in a terrain awareness warning system. The apparatus includes a first input for a first signal from an instrument measuring a height of an aircraft, a second input for a second signal from an instrument measuring a location of the aircraft, a third input for a third signal from an instrument providing information about geographic features of terrain surrounding the aircraft, and a fourth input for a fourth signal from an instrument measuring a flight path of the aircraft. The apparatus includes means for employing the signals from the first through fourth inputs to calculate an effective height of the aircraft relative to at least the third input, and a screen display for graphically displaying the results of the calculation.
Implementations of the apparatus may include one or more of the following. The instrument measuring height and location of the aircraft may include an altimeter. The instrument providing information about geographic features of terrain surrounding the aircraft, as well as the instrument measuring a flight path of the aircraft, may be aids to navigation, such as a global positioning system unit. The apparatus may further include a conventional TAWS altitude display and means to toggle the screen display between the conventional TAWS altitude display and the screen display for graphically displaying the results of the calculation. The first through fourth inputs may form at least a portion of a parallel data bus or a serial data stream.
In a further aspect, the invention is directed towards a method of performing terrain awareness warning for an aircraft. The method includes steps of collecting data about terrain features in the vicinity of an aircraft, collecting data of the lateral distance and bearing of the terrain features from the aircraft, collecting data of the height and flight path of the aircraft, calculating a projected height of the aircraft at the location of each of the terrain features based on the collected data of the height and flight path of the aircraft, and generating result signals based on the projected height, the collected data of terrain features, and the bearing of the terrain features. The method further includes displaying colored indications on a display screen, with respect to bearing, based on the generated result signals.
In still a further aspect, the invention is directed towards a method for providing an indication of lateral aircraft position relative to an obstruction in a terrain awareness warning system. The method includes steps of receiving a first datum indicative of the bearing of an obstruction relative to an aircraft, receiving a second datum indicative of a lateral distance of the obstruction from the aircraft, and receiving third data indicative of a flight path of the aircraft. The method further includes steps of calculating a projected flight path of the aircraft relative to the obstruction using the first through third data and determining a distance between the projected flight path and the obstruction at a series of points along the projected flight path. The method includes steps of generating a result signal based on the determined distance, and displaying a colored indication on a display screen based on the generated result signal with respect to the bearing.
Advantages of the invention may include one or more of the following. The invention allows for more accurate terrain displays, giving the pilot a more reliable indicator of the relative danger of forward terrain. The invention provides this increased accuracy in part by taking into account factors, such as the flight path angle of the aircraft, when calculating and displaying alerts. As a result, false warnings are eliminated and dangerous situations that would not have been noticed by prior systems are avoided.
Other advantages will be apparent from the description that follows, including the figures and the claims.